The present invention relates to high internal phase polymeric emulsion (“HIPPE”) compositions and to processes for their creation.
Emulsions based on water/oil/surfactant systems have been extensively investigated during the past few decades. (e.g., see Lissant, Colloid Interface Sci., 22:462 (1966); Lissant et al., J. Colloid Interface Sci., 42:201 (1973); Princen, Colloid Interface Sci., 71:55 (1979); Westesen et al., Colloids Surf. A, 78:125 (1993); Groeneweg et al., Colloids Surf A, 91:207 (1994); Kunieda et al., C. Langmuir, 12:2136 (1996); Ozawa et al., J. Colloid Interface Sci., 188:275 (1997); Mork et al., J. Surfactants Deterg., 4:127 (2001).) High internal phase emulsions (HIPE) can be achieved in these systems, in which the dispersed phase is present in a volume fraction exceeding 0.74, i.e., the critical packing fraction of a face-centered-cubic (fcc) crystal. At these high volume fractions, it is no longer possible to closely pack monodisperse spheres, and therefore in order to maintain the high volume fraction, droplets with a narrow size distribution will rearrange into polyhedral structures. (e.g., see Lissant et al., J. Colloid Interface Sci., 42:201 (1973); Kunieda et al., C. Langmuir, 12:2136 (1996); Ozawa et al., J. Colloid Interface Sci., 188:275 (1997).)
Multiple efforts have been made more recently to synthesize polymer-based HIPE, generally referred to as poly(HIPE) or HIPPE (e.g., see Haney et al., Macromolecules, 24:117 (1991); Sherrington, Makromol. Chem. Symp., 70:303 (1991)), owing to the potential advantages these structures may have in many practical applications, such as membranes, foams, barriers, etc. The emulsification process in such a polymer-based HIPE is analogous to that of water-in-oil emulsions. An oil, such as petroleum ether or a low molecular weight compound phase, is generally dispersed dropwise in a solution of monomer, solvent, and surfactant so that an emulsion of up to 90% oil in the monomer bath can be obtained. (e.g., see Haney et al., Macromolecules, 24:117 (1991); Sherrington, Makromol. Chem. Symp., 70:303 (1991); Cameron et al., J. Chem. Soc., Faraday Trans., 92:1543 (1996); Cameron et al., Macromolecules, 30:5860 (1997).) Subsequently, the continuous monomer phase is polymerized and the solvent removed. The most extensively used monomers are styrene or divinylbenzene (DVB), which can be polymerized by a free radical polymerization process (e.g., see Tai et al., Polym. Eng. Sci., 41:1540 (2001); Cameron et al., Colloid Polym. Sci., 274:592 (1996); Hoisington et al., Polymer, 38:3347 (1997); Duke et al., Polymer, 39:4369 (1998); Cameron et al., J. Mater. Chem., 10:2466 (2000); Tai et al., Polymer, 42:4473 (2001); Tai et al., Polym. Eng. Sci., 41:1540 (2001)). Ionic, nonionic, and polymeric surfactants have also been used. (e.g., see Reynolds et al., J. Phys. Chem. B, 104:7012 (2000); Dickinson et al., J. Colloid Interface Sci., 224:148 (2000); Pena et al., J. Colloid Interface Sci., 244:154 (2001); Pons et al., Colloid Polym. Sci., 275:769 (1997).) By following this procedure, a blend is produced in which the dispersed phase is liquidlike, and foams with very low density can be obtained by extracting this phase. (e.g., see Sherrington, Makromol. Chem. Symp., 70:303 (1991); Cameron et al., J. Mater. Chem., 10:2466 (2000); Tai et al., Polymer, 42:4473 (2001); Tai et al., Polym. Eng. Sci., 41:1540 (2001); Bhumgara, Filtr. Separat, 32:245 (1995); Benicewicz et al., J. Radioanal. Nuc. Chem., 235:31 (1998); Busby et al., Biomacromolecules, 2:154 (2001).)
Mezzenga et al., (e.g., see Mezzenga et al., Macromolecules, 36:4457 (2003) describes a solvent-based technique allowing the synthesis of HIPPE structures in which both phases can be polymeric without the need of polymerization. By following this technique, which involves appropriate selection of polymers, solvents, and block copolymer surfactant, HIPPE structures were produced in which a continuous minority phase is present in a volume fraction as low as 0.13. This technique was shown to be highly desirable for producing blends in which unique Theological, electrical, and barrier properties of the minority, percolating phase can be exploited. However, a less than desirable control of mean particle size has yet to be achieved with this technique, a limitation that represents a drawback if optical, transport, and mechanical properties of the final blend need to be uniform and controlled.
In principle, particle size can be controlled if colloidal latex particles with a narrow size distribution are used as discrete phase precursors to form HIPPE compositions. These latex particles are readily available today, owing to the large number of applications in which they are used, ranging from coating, rubber modification, and ion-exchange technologies (e.g., see Keddie, Mater. Sci. Eng., R., 21:101 (1997)) to photonic or colloidal crystal applications (e.g., see Egen et al., Chem. Mater., 14:2176 (2002); Ye et al., Appl. Phys. Lett., 79:872 (2001); Reese et al., J. Colloid Interface Sci., 232:76 (2000)) Indeed, substantial advances have been made in the production of nearly monodisperse colloidal spheres as well as on colloidal crystallization. A reason is that for these applications colloidal particles with a narrow size distribution are required in order to achieve well-formed crystals starting from a colloidal dispersion. (e.g., see Park et al., Langmuir, 15:266 (1999); Yin et al., Adv. Mater., 14:605 (2002).) One route to self-assemble colloidal particles into dense arrays is to make use of attractive depletion interactions, induced by dispersing colloidal particles and dissolving polymer chains in the same solution. (e.g., see Asakura et al., J. Chem. Phys., 22:1255 (1954); Vrij, A. Pure Appl. Chem., 48:471 (1976)) In this way, the polymer chains, excluded from a Rg-thick corona around the colloids, where Rg is the radius of the gyration of the polymer, gain entropy on the approach of particles, whereas only a minor entropy loss is suffered by the colloidal particles. Other strategies to bind colloidal particles together have focused on surface interactions, by using charged particles (e.g., see Airenberg et al., Phys. Rev. Lett., 84:2997 (2000)) or core-shell latexes (e.g., see Cardoso et al., Colloids Surf A., 144:207 (1998)). Under the influence of these forces, colloidal systems have been shown to undergo complex phase transitions, and intriguing phase diagrams have been demonstrated (e.g., see Anderson et al., Nature (London), 416:6883 (2002)) However, all these methods have led, in the best case, to closely packed arrays of colloidal particles in a body centered cubic (bcc), hexagonal close packed (hcp), or face centered cubic (fcc) structure. As a consequence, if HIPPE structures without voids are to be produced by these methods, the volume fraction cannot exceed 0.74 for the dispersed phase, and the continuous phase, formed by another polymer, has to be present at a volume fraction equal to or beyond 0.26.
As such, methods for the economical production of stable high internal phase polymeric emulsions, where both discrete and continuous phases are composed of polymeric fluids or solids, have been limited.
Therefore, there exists a need to produce HIPPE compositions, wherein the morphologies of both the continuous and dispersed phases can be controlled.